1. Field of the Invention
This invention relates to a starter motor, and more particularly to a starter motor for driving a pinion for engagement with a ring gear of an engine to start the engine.
2. Description of the Prior Art
Starter motors of the so-called overhang type are conventionally well known. An exemplary one of such starter motors is disclosed, for example, in Japanese Utility Model Laid-Open No. 6679/1986. The exemplary starter motor is shown in FIGS. 10 and 11.
Referring to FIGS. 10 and 11, the conventional starter motor of the overhand type shown includes a front bracket 1 of an outer casing or motor frame in which an opening 2 is formed. An extension or output rotary shaft 3 of an armature rotary shaft of a dc motor (not shown) disposed in the inside of the motor frame extends outwardly through the opening 2 of the front bracket 1. A pinion moving member 4 is fitted for sliding movement on and for rotation relative to the output rotary shaft 3 with a pair of bearings 5 interposed therebetween. The pinion moving member 4 is supported also for rotation and for axial sliding movement by means of a bearing 6 mounted on an inner face of the front bracket 1 adjacent the opening 2 to thus support the output rotary shaft 3 on the motor frame.
The pinion moving member 4 has a pinion 4a formed on an outer periphery of a front end portion (right-hand end portion in FIG. 10) thereof while a rear end thereof terminates in a clutch inner member 7a which is a component of an overrunning clutch device 7. Meanwhile, an outer periphery of the pinion moving member 4 between the pinion 4a and the clutch inner member 7a serves as a sliding supporting face 4b at which the pinion moving member 4 is supported for axial sliding movement by the bearing 6.
The overrunning clutch device 7 further includes a clutch outer member 7b and a plurality of rollers 7c for transmitting turning force from the clutch outer member 7b to the clutch inner member 7a. An oil seal 8 is fitted around the outer periphery of the pinion moving member 4 forwardly of the bearing 6. A dust protective cap 9 is removably mounted at a front end of the pinion moving member 4. A stopper 10 is mounted at an end of the output rotary shaft 3 and prevents the pinion moving member 4 from coming off from the output rotary shaft 3. A ring gear 11 of an engine, not shown, is positioned in an opposing relationship to an outer periphery of a front end portion of the output rotary shaft 3.
In operation, the overrunning clutch device 7 will be shifted forwardly in the direction of an arrow mark 12 in FIG. 10 by way of a shift lever (not shown) of a vehicle in which the engine is installed. Upon such shifting movement of the overrunning clutch device 7, also the pinion moving member 4 is slidably mounted in an integral relationship with the overrunning clutch device 7 on the output rotary shaft 3 so that the pinion 4a thereof extending outwardly through the opening 2 of the front bracket 1 is brought into meshing engagement with the ring gear 11 of the engine as shown in FIG. 11. The dc motor is energized just before the pinion 4a is brought into meshing engagement with the ring gear 11, and rotation of the armature rotary shaft thereof is transmitted from the clutch outer member 7b to the clutch inner member 7a by way of the rollers 7c of the overrunning clutch device 7 to rotate the pinion moving member 4 to start the engine by way of the pinion 4a and the ring gear 11.
When the pinion moving member 4 is rotated at a high speed by the engine after starting of the engine but before returning of the pinion moving member 4 in the direction opposite to the direction of the arrow mark 12 to its home position by a spring means, not shown, the clutch inner member 7a of the overrunning clutch device 7 is rotated at a higher speed than the clutch outer member 7b. Consequently, the rollers 7c are brought out of meshing engagement with the clutch inner member 7a and the clutch outer member 7b to allow the clutch inner member 7a to rotate idly with respect to the clutch outer member 7b. Thus, the overrunning clutch device 7 serves as a one-way clutch which has a function to transmit turning force only in one of the two opposite directions, and high speed rotation of the pinion moving member 4 is not transmitted to the dc motor.
While the oil seal 8 serving as a waterproof and dust tight structure of the starter motor is not described in detail in Japanese Utility Model Laid-Open No. 6679/1986 mentioned hereinabove, such a conventional oil seal as shown in FIG. 12 may be employed as the oil seal 8. Referring to FIG. 12, the conventional oil seal 8 shown includes a mounting ring 8a made of iron and having a substantially L-shaped cross section, and a rubber seal element 8b having a V-shaped cross section and securely mounted on an inner periphery of the mounting ring 8a. As apparently seen in FIG. 12, the oil seal 8 having such construction as described just above is mounted by force fitting on an inner periphery of the opening 2 of the front bracket 1 which is formed axially outwardly of and has a smaller diameter than another inner periphery of the opening 2 of the front bracket 1 in which the bearing 6 is fitted. The oil seal 8 is spaced forwardly from the bearing 6, and the opening side of the V-shaped seal element 8b is directed outwardly of the opening 2 while a radially inward lip portion 8c thereof is held in contact with the outer periphery of the pinion moving member 4.
A conventional starter motor of the overhand type which includes such a waterproof and dust tight structure as described above has a drawback that water is likely to gather in the V-shaped seal element 8b of the oil seal 8. Particularly where the starter motor is mounted in a vertical orientation on an engine such that the pinion 4a is located upwardly while the dc motor is located downwardly, water may be received in the V-shaped seal element 8b. Once water gathers in the seal element 8b of the oil seal 8 in this manner, it will readily advance into the inside of the front bracket 1 due to a breathing action by heat or due to vibrations and will thus cause rust on the bearing 6 which may be in the form of a ball bearing. Such rust will deteriorate sliding movement of the pinion moving member 4 with respect to the output rotary shaft 3 coupled to the dc motor. Or worse, water may advance into the inside of the dc motor and cause a failure in operation of the dc motor.
A starter motor is also conventionally known which is constructed such that water which eventually gathers in the motor is removed from within the motor by way of a water drain hole. The starter motor of the type just mentioned is shown in FIG. 13. Referring to FIG. 13, the starter motor shown includes a motor body 51 composed of an armature 52, an armature rotary shaft 53, a plurality of field coils 54, a plurality of armature coils 55, a plurality of magnetic poles 56, a yoke 57 and so forth. A pinion 58 for engaging with a ring gear (not shown) of an engine (not shown) is mounted on an output rotary shaft 59 which may be in the form of a forward extension of or may be coupled to the armature rotary shaft 53. The pinion 58 is operatively coupled to the output rotary shaft 59 by way of an overrunning clutch device 60 which includes a clutch outer member 61 and a clutch inner member 62 formed in an integral relationship with the pinion 58. A rear end portion of the armature rotary shaft 53 is supported for rotation on a rear bracket 63 by way of a bearing 65 while a front end portion of the output rotary shaft 59 is supported for rotation on a front bracket 64 by way of another bearing 66. A sleeve bearing 67 is interposed between the pinion 58 and the output rotary shaft 59. An electromagnetic switch 68 is disposed in parallel to the armature rotary shaft 54 and actuates, upon closing of a starter switch not shown, a shift lever 69 to push the pinion 58 axially outwardly of the motor body 51 and close contacts, not shown, to supply electric power to the motor body 51.
The rear bracket 63 and the front bracket 64 cooperate to form an outer casing which surrounds the motor body 51 together with the yoke 57, and an oil seal 70 for waterproofing is interposed between the front bracket 64 and the overrunning clutch device 60 while a radial water discharging hole 71 is formed in the front bracket 64 forwardly of the oil seal 70.
With this starter motor, even if water comes to a location around the pinion 58 from the engine side, it is prevented from advancing into the inside of the starter motor by the oil seal 70 on the outer periphery of the overrunning clutch device 60 or pinion 58 and is discharged by way of the water discharging hole 71.
However, if water comes to a location around the pinion 58 from a transmission side of the engine when the motor body 51 is in a high temperature condition, water is sometimes admitted into the outer casing of the starter motor due to a capillary phenomenon along the overrunning clutch device 60. Consequently, water gathers around the motor body 51 and causes rust on the motor body 51, which will deteriorate operation of the starter motor.
In order to discharge water which may possibly gather in the inside of the outer casing of the starter motor, a water drain hole 72 is formed at a lower or bottom portion of a side wall of the outer casing, that is, the rear bracket 63. Actually, however, such water drain hole 72 is not very effective to discharge water gathering in the inside of the starter motor. Or rather, splashed water may be admitted into the inside of the starter motor by way of the water drain hole 72, resulting in deterioration in operation of the starter motor.
In the case of the starter motor which is mounted on the engine in a horizontal orientation wherein the axis of the armature rotary shaft 53 extends in a horizontal direction, the water drain hole 72 is formed at a bottom portion of the side wall of the rear bracket 63 as described above. However, where the starter motor is mounted in a vertical orientation wherein the axis of the armature rotary shaft 53 extends in a vertical direction as shown in FIG. 14, the water drain hole 72 is conventionally formed at a different bottom portion, that is, at an axial end wall of the rear bracket 63 as shown in FIG. 14. Also the arrangement is not effective to prevent the motor body from being wet with water admitted into the inside of the starter motor from the transmission side.